Countless individuals suffer from the ocular disease glaucoma. This condition describes a destruction of optic nerve cells and deterioration of eyesight as a result of increased intraocular pressure. The pressure is caused in part by a buildup of carbon dioxide in the eye. An enzyme that aids in the production of CO2 is human carbonic anhydrase II (hCAII). This Zn2+ containing metalloenzyme (FIG. 1) catalyzes the reversible hydration of carbon dioxide to bicarbonate and is commonly found in living organisms.
Sulfonamide compounds have been shown to selectively inhibit hCAII even at low concentratons.1 Therefore, inhibition of hCAII with sulfonamides constitutes one of the most physiological approaches for treatment of glaucoma. In 1958 Beasley et al. reported the in vitro binding of 4-carboxybenzene sulfonamide (CBS) to the carbonic anhydrase (CA) enzymes.2 Since then, many other hCAII inhibitors based on this moiety have been reported.3-5 A remarkable increase in the hCAII inhibition activity was observed for simple aliphatic esters of CBS.5 Also, it is now extensively documented that significant enhancement of CA inhibition can be achieved through coupling the primary recognition aromatic sulfonamide motif with secondary binding elements.3,5-9 The mechanism for inhibition of hCAII by CBS involves coordination of the sulfonamide group (as the anion) to the zinc atom in the active site of hCAII to form a complex in an exothermic reaction. 6, 10, 11.
In ophthalmic diseases such as glaucoma, treatment with conventional liquid eye drops is an inefficient mode of therapy because of lachrymal drainage losses. Because of the high elimination rate, only a very small amount of about 1-3% of the dosage actually penetrates through the cornea and is able to reach intraocular tissues.12-14 Nanoparticles provide a promising potential as drug carriers for ophthalmic applications. The colloidal nanoparticles may be applied in liquid form just like eye drop solutions. After optimal drug binding to the nanoparticles, the ocular bioavailability of many drugs is significantly enhanced in comparison to normal aqueous eye drop solutions.12 Also, smaller particles improve patient comfort during administration as a scratchy feeling tends to occur with larger particles. Nanoparticles and microspheres of various synthetic polymers such as poly-butylcyanoacrylate,15,16 polylactic acid,17 polymethylmethacrylate,16 and so forth as well as natural biocompatible polymers like albumin18,19 have been used for ophthalmic drug delivery applications.